Fluorine-containing polymers have excellent chemical resistance, solvent resistance, heat resistance and antifouling property and thus have been used as a starting material of various products utilizing these properties in various industrial fields such as automobile industry, semiconductor industry, chemical industry and coatings.
The production of these fluorine-containing polymers has been performed by an emulsion polymerization, a suspension polymerization or a solution polymerization of a fluoroolefin. Generally, a surfactant is used in the emulsion polymerization method, and as the amount of the surfactant to be used increases, the number of polymer particles formed in the initial period of the emulsion polymerization increases. As a result, the polymerizing speed becomes fast and the production efficiency of the fluorine-containing polymer improves. However, the use of a large amount of surfactant tends to decrease various properties such as water resistance of the obtained fluorine-containing polymer. Therefore, the development of the production method which can perform a polymerization efficiently in the presence of a small amount of surfactant and does not have a bad influence on various properties of the fluorine-containing polymer has been desired.
In such circumstances, a production method of a fluorine-containing polymer in which a surfactant of a straight chain aliphatic sulfonates is used, in order to replace an expensive ammonium perfluorooctanoate which is generally used in the emulsion polymerization of a fluorine-containing polymer, is proposed (Patent Document 1). However, this method has a problem that the number of generated particles is small.
Further, a production method using an alkyl phosphoric acid or an ester thereof (Patent Documents 2 and 3) and a method using a compound in which a phosphoric acid, a sulfonic acid, a carboxylic acid or the like is bonded to a quaternary carbon atom (Patent Document 4) are proposed as a method using a non-fluorine-containing surfactant.
However, in the case of using an alkyl phosphoric acid or an ester thereof, the method is not always enough in terms of the number of generated particles, a polymerizing speed, a molecular weight of the obtained polymer, a polymer concentration of an aqueous dispersion, a polymerizing temperature, a polymerizing pressure and the like. Also, in the method using a compound in which a phosphoric acid, a sulfonic acid, a carboxylic acid or the like is bonded to a quaternary carbon atom, a further increase of generated particles is desired.
On the other hand, fluorine-containing materials are expensive, and the amount to be used thereof is tried to be decreased. One example is a method of seed-polymerizing ethylenically unsaturated monomer such as an acrylic acid with fluorine-containing polymer particles (Patent Document 5).